Note: Descriptions are shown in the official language in which they were submitted.
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Method for diagnosing a self-blowout circuit breaker, and
diagnosis apparatus
TECHNICAL FIELD
The invention relates to methods and devices for diagnosing
circuit breakers. The invention relates in particular to
methods and devices, with which the state of a burn-off
nozzle of a self-blast circuit breaker can be determined.
BACKGROUND
Circuit breakers are safety elements which can be used at
present in the field of medium and high voltage in
alternating voltage networks for interrupting nominal and
short-circuit currents. The circuit breaker technology can
also be used in direct-current networks. Circuit breakers
can, for example, be configured as vacuum circuit breakers
or as gas-filled circuit breakers. At the high-voltage,
gas-filled circuit breakers are frequently used. The
filling gas can, for example, comprise sulfur hexafluoride
(SF6) as insulating and quenching gas.
In most cases, a circuit breaker has two switching contacts
which are in contact with one another in the closed state
of the circuit breaker. For breaking, the two contacts are
moved away from one another and in doing so an arc burning
between the contacts is formed. For successful switching-
off of the current, it is crucial to quench this arc
between the switching contacts. For this purpose, in the
case of puffer circuit breakers and in the case of self-
blast circuit breakers, quenching and insulating gas is
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blown onto the arc and cools it. The filling gas, with
which the puffer circuit breaker or self-blast circuit
breaker is filled, can be composed partially or completely
of the quenching gas. For this purpose, this gas must on
the one hand be capable of cooling and quenching the arc,
and after quenching the arc should prevent an arc-back or
restriking between the contacts.
In self-blast circuit breakers, the energy converted in the
arc is utilised to build up the gas pressure necessary for
blowing onto the arc. The arc between the switching
contacts can in this case be guided, during the switching-
off operation, in burn-off nozzles made of an insulating
material such as polytetrafluoroethylene (PTFE) or another
suitable material, which evaporates under the influence of
the arc and thus increases an overpressure of the gas. In
today's high-voltage networks self-blast circuit breakers
with sulfur hexafluoride (SF6) as insulating medium are
widely used.
Manufacturers of circuit breakers prescribe in their
maintenance guidelines that the gas compartment of a self-
blast circuit breaker is to be opened at specific intervals
or after a specific number of switching cycles. The reason
for this is so as to inspect the burn-off of contact and
nozzle systems. In the past, a reliable method for
determining the contact burn-off using the dynamic
resistance measurement was established. Nevertheless,
customarily the self-blast circuit breakers have to be
opened to inspect the nozzle burn-off of the burn-off
nozzle made of insulant.
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This entails several disadvantages for the operator of the
self-blast circuit breaker. The opening of the self-blast
circuit breaker is time- and labour-consuming and thus
results in high costs. Furthermore, the switchgear in which
the self-blast circuit breaker is used has to be at least
partially shut down. After opening the housing of a self-
blast circuit breaker, there may be an increased
susceptibility to faults, which may be due to the risk of
incorrect reassembly or the introduction of foreign matter.
A non-invasive and reliable method for determining the
nozzle burn-off could delay or even entirely avoid opening
of the interrupting chamber. One approach for non-invasive
determination of the nozzle burn-off can consist in
measuring a frequency response. In this case, the self-
blast circuit breaker can be subjected as test object to an
electrical or mechanical signal as stimulus and its
reaction can be determined in a frequency response analysis
(FRA). In this way, for example the burn-off of nozzle
material can be determined. However, the implementation of
such an approach is complex. The implementation may involve
difficulties in particular on use in the field.
A further approach for non-invasive determination of the
nozzle burn-off is the temporally resolved measurement of
the currents occurring in the network, in order
subsequently to calculate the nozzle burn-off occurring at
the present current with the aid of simulations. The
implementation of this approach would, however, require
extensive fitting of the existing protection and control
system with suitable units for data acquisition and data
storage, resulting in considerable installation complexity
and considerable installation costs.
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Methods for monitoring circuit breakers, as described, for
example, in DE 196 04 203 Al, are limited to observing the
drive device or the movable contact of the circuit breaker
and do not allow the nozzle burn-off to be inferred.
SUMMARY
There is therefore still a need for methods and devices
with which a nozzle burn-off can be assessed without the
interrupting chamber of the self-blast circuit breaker
having to be opened. There is in particular a need for such
methods and devices which can be simply incorporated in
existing maintenance activities and entail only little
additional cost and time expenditure.
The object of the invention is to specify methods and
devices which provide improvements with regard to the
problems described.
In a method of diagnosing a self-blast circuit breaker, a
switching operation of the self-blast circuit breaker is
triggered to initiate a pressure wave in a filling gas of
the self-blast circuit breaker. A pressure as a function of
time which occurs in at least one region of the self-blast
circuit breaker in response to the switching operation is
detected. A state of a burn-off nozzle of the self-blast
circuit breaker which is burnt off in a switching operation
under load for blowing the filling gas onto a switching arc
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is determined in dependence on the pressure as a function
of time.
In the method, the state of the burn-off nozzle is inferred
from the pressure as a function of time. The detection of
the pressure profile can take place without the self-blast
circuit breaker having to be disassembled and/or the
interrupting chamber opened. The pressure build-up required
for the measurement can be generated by the compression of
a volume in the circuit breaker itself, for example under
the action of the drive of the self-blast circuit breaker
or in another manner. In this case, the transient pressure
profile is influenced by a flow resistance of the nozzle
system. The detection of the pressure profile can take
place on the assembled self-blast circuit breaker, so that
the method can be performed time-efficiently and cost-
effectively. The circuit breaker has merely to be isolated
for a short period of time in which the self-blast circuit
breaker is being maintained. The geometry of the burn-off
nozzle influences pressure waves, for example sound waves,
which propagate in the filling gas after a switching
operation without electric load, so that based on the
pressure profile it can be reliably determined whether the
burn-off of the burn-off nozzle is so severe that a
disassembly of the self-blast circuit breaker is required.
The state of the burn-off nozzle can be determined based on
a transient pressure variation which is detected in
response to the switching operation in a time interval. The
pressure variation varies in dependence on the nozzle burn-
off. The existing connection for the gas filling can be
utilised as measuring position. It is thus possible to
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perform the inspection of the nozzle system in the course
of standard maintenance directly in situ.
The pressure as a function of time can be detected at a
filling port of the self-blast circuit breaker which is
spaced from the burn-off nozzle. This filling port is
easily accessible also in the assembled state of the self-
blast circuit breaker. The measurement can take place
without a modification of the circuit breakers being
necessary.
The switching operation with which the pressure wave is
initiated can be performed without electric load.
The measurement and evaluation can be performed
automatically using a diagnostic device, without the self-
blast circuit breaker having to be converted for this
purpose and brought into a measuring laboratory. The
measurement and evaluation can be performed using a
compact, mobile diagnostic device. A pressure sensor of the
mobile diagnostic device can be removably mounted on the
self-blast circuit breaker such that it detects the
pressure profile.
In the method, a contact separation of contacts of the
self-blast circuit breaker can be detected. The time
interval in which the transient pressure variation is
evaluated to obtain information about the nozzle burn-off
can be set in dependence on a time at which the contact
separation takes place. Alternatively or additionally, the
data acquisition of the pressure profile can be set in
dependence on the time at which the contact separation
takes place.
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A mechanical drive of the self-blast circuit breaker can be
monitored to detect the contact separation. For this
purpose, a rotation angle sensor can be mounted on a drive
shaft of the self-blast circuit breaker.
In the method, a pressure and a temperature of the filling
gas can be detected before the switching operation is
triggered. The time interval in which the transient
pressure variation is evaluated to obtain information about
the nozzle burn-off can be set in dependence on the
detected pressure and the detected temperature of the
filling gas. In this way, the speed of sound or a variation
of the speed of sound in the filling gas can be taken into
account. The speed of sound influences the time interval in
which pressure variations influenced by the geometry of the
burn-off nozzle are detectable at a measuring position, for
example at the filling port of the self-blast circuit
breaker. The time interval can be set further in dependence
on the geometry of the self-blast circuit breaker, in order
to take into account the distance between burn-off nozzle
and measuring position.
The state of the burn-off nozzle can be determined in
dependence on a time integral of the detected transient
pressure variation. Since a sign of the pressure variation
can depend on the nozzle burn-off, the state of the burn-
off nozzle can be reliably determined in this way by simple
processing.
The state of the burn-off nozzle can be determined in
dependence on a spectral component of the detected pressure
as a function of time. The pressure profile which is
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detected in a time interval after triggering of the
switching operation can be subjected to a spectral
analysis. For example, a Fourier transformation can be
carried out. Alternatively or additionally, the pressure
profile can be subjected to a filtering in order to
suppress undesired signal components which may be caused,
for example, by reflections of sound waves between the side
walls of the self-blast circuit breaker.
The determination of the state of the burn-off nozzle can
take place automatically and computer-aided. For this
purpose, the construction type of the self-blast circuit
breaker and/or other information which identifies the self-
blast circuit breaker can be input via a user interface of
a diagnostic device by a user input. One or more
characteristic quantities which depend on the detected
pressure profile can be compared with characteristic
quantities stored in a database for the construction type,
in order to determine the state of the burn-off nozzle. In
one configuration, for each construction type, a plurality
of time-dependent pressure profile curves can be stored in
the database. The pressure profile detected at the self-
blast circuit breaker can be compared with the stored
pressure profile curves, in order to determine whether the
burn-off of the burn-off nozzle has progressed to such an
extent that visual inspection or a replacement of the self-
blast circuit breaker is required. In a further
configuration, a spectral component of the detected
pressure profile can be compared with one or more threshold
values stored in the database for this construction type.
In this way, it can be determined whether the burn-off of
the burn-off nozzle has progressed to such an extent that a
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visual inspection or a replacement of the self-blast
circuit breaker is required.
The determined state of the burn-off nozzle can be selected
from a group, comprising a first state, which allows
operation of the self-blast circuit breaker to be
continued, and a second state, which requires a visual
inspection of the burn-off nozzle of the self-blast circuit
breaker.
The method can be performed using a diagnostic device, in
particular a mobile diagnostic device, on the assembled
self-blast circuit breaker. The method can be performed
non-invasively without opening the interrupting chamber of
the self-blast circuit breaker.
According to a further embodiment, a diagnostic device for
self-blast circuit breakers is specified. The diagnostic
device comprises an interface for receiving pressure data
which indicate a pressure as a function of time in at least
one region of the self-blast circuit breaker in response to
a switching operation of the self-blast circuit breaker.
The diagnostic device comprises a control coupled to the
interface and configured to determine, in dependence on the
pressure data, a state of a blow-off nozzle of the self-
blast circuit breaker which is burnt off in a switching
operation under load. The diagnostic device can be
configured as a mobile diagnostic device.
The effects achieved with the diagnostic device correspond
to the effects achieved with the method.
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The diagnostic device can comprise a pressure sensor
configured to be detachably coupled to the interface. The
pressure sensor can have a coupling structure configured
for mounting to a filling port of the self-blast circuit
breaker.
The diagnostic device can comprise a further sensor or a
plurality of further sensors for monitoring a contact
separation. For example, the diagnostic device can comprise
a rotation angle sensor for detecting a rotation angle of a
drive shaft of the self-blast circuit breaker. The
diagnostic device can comprise further sensors for
detecting the contact separation. For example, the
interruption of a weak current by the circuit breaker can
be utilised or monitored. The control is coupled to the
further sensor and configured to determine the state of the
burn-off nozzle in dependence on a pressure variation in a
time interval which is a function of a time of the contact
separation.
The diagnostic device can comprise a memory, to which the
control is coupled. The memory can contain, for a plurality
of construction types of self-blast circuit breakers,
respective information on a pressure as a function of time
after triggering of a switching operation, with which
information the control automatically evaluates the
pressure profile detected at the self-blast circuit
breaker.
The diagnostic device can be configured to perform the
method according to an exemplary embodiment. In this case,
the control can perform the various evaluating steps of the
method in order to determine, with the detected pressure
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profile, whether the burn-off of the burn-off nozzle has
progressed to such an extent that a visual inspection or a
replacement of the self-blast circuit breaker is required.
The switching operation which is triggered to initiate a
pressure wave in the filling gas can transfer the self-
blast circuit breaker from a closed state into an open
state. The switching operation can be triggered by the
diagnostic device.
Methods and devices for diagnosing self-blast circuit
breakers can be used to inspect circuit breakers in medium-
voltage networks and high-voltage networks.
BRIEF DESCRIPTION OF THE FIGURES
The invention is explained below using preferred
embodiments with reference to the drawings.
FIG. 1 is a schematic illustration of a self-blast circuit
breaker with a mobile diagnostic device according to an
exemplary embodiment.
FIG. 2 shows a sectional view of an arcing chamber of the
self-blast circuit breaker for explaining a method
according to an exemplary embodiment.
FIG. 3 shows an enlarged view of a part of the arcing
chamber in a state without nozzle burn-off.
FIG. 4 shows an enlarged view of the part of the arcing
chamber in a state with more severe nozzle burn-off.
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FIG. 5 shows pressure profiles which are evaluated in
methods and mobile diagnostic devices according to
exemplary embodiments, in order to determine a state of a
burn-off nozzle.
FIG. 6 shows pressure profiles which are evaluated in
methods and mobile diagnostic devices according to
exemplary embodiments, in order to determine a state of a
burn-off nozzle.
FIG. 7 shows pressure profiles which are evaluated in
methods and mobile diagnostic devices according to
exemplary embodiments, in order to determine a state of a
burn-off nozzle.
FIG. 8 shows pressure profiles for different speeds of a
contact pin without nozzle burn-off.
FIG. 9 shows pressure profiles for different speeds of a
contact pin with more severe nozzle burn-off.
FIG. 10 is a flow diagram of a method according to an
exemplary embodiment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
In the figures, similar or identical reference symbols
denote similar or identical elements.
While methods and diagnostic devices according to exemplary
embodiments are explained using self-blast circuit breakers
with exemplary configurations, the methods and diagnostic
devices can be used in self-blast circuit breakers with a
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large number of other configurations. The illustrated
configurations of self-blast circuit breakers are to be
understood as merely illustrating operating principles of
self-blast circuit breakers. The term "self-blast circuit
breaker" is used here synonymously with the terms "self-
blast breaker" or "self-blaster" likewise commonly used in
the art.
FIG. 1 is a schematic illustration of a self-blast circuit
breaker 1 with a mobile diagnostic device 20 according to
an exemplary embodiment. The self-blast circuit breaker 1
is a circuit breaker for a medium-voltage network or a
high-voltage network. Even though only one self-blast
circuit breaker 1 is illustrated, a plurality of self-blast
circuit breakers can be combined in a combined arrangement
or "battery" of self-blast circuit breakers. In this case,
the mobile diagnostic device 20 can automatically perform
the described diagnostic device 20 can automatically
perform the described diagnostic functions for determining
a nozzle burn-off for each of the plurality of self-blast
circuit breakers.
The self-blast circuit breaker 1 has a housing 2. A first
contact 3 and a second contact 4 are provided in the
housing. In the closed state of the self-blast circuit
breaker 1, the first contact 3 and the second contact 4 are
in contact with one another. In order to transfer the self-
blast circuit breaker 1 into the open state, at least one
of the contacts is moved. Mechanical components such as a
drive rod 5, which is coupled to a motor via a gearing, are
provided. A drive shaft 6 can cause a movement of one of
the contacts via the drive rod 5, in order to transfer the
self-blast circuit breaker 1 into the open state. By way of
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example, the second contact 4, which can be formed as a
finger contact, can be moved together with a burn-off
nozzle 11 relative to the first contact 3, which can be a
fixed contact pin.
The self-blast circuit breaker 1 is configured as a gas-
filled circuit breaker. A filling gas is contained in an
interior 8 of the housing 2. By way of example, sulfur
hexafluoride (SF6) can be used as the filling gas, or the
filling gas can consist substantially of sulfur
hexafluoride. Other insulating and quenching gases can be
used. When the in a state in which the self-blast circuit
breaker 1 is under electric load, the self-blast circuit
breaker 1 is transferred into an open state, the filling
gas quenches an arc burning between the first contact 3 and
the second contact 4. For this purpose, the filling gas or
a mixture of the filling gas and the gas which is produced
by nozzle burn-off is blown onto the arc. The filling gas
can be blown onto the arc via an opening 10 which is
situated in the vicinity of the place at which the arc is
burning. For an efficient pressure build-up, the burn-off
nozzle 11 is provided in the self-blast circuit breaker 1.
The burn-off nozzle 11 is formed from an insulating
material or insulant which partially evaporates under the
influence of the arc. This process is also called "burning-
off" or "burn-off" of the burn-off nozzle 11. The resulting
partial pressure can be used for blowing filling gas onto
the arc. The burn-off nozzle 11 can be formed, for example,
from polytetrafluoroethylene (PTFE) or another suitable
ins ulant.
For maintenance work, the self-blast circuit breaker 1 has
a filling port 9, via which the filling gas can be
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refilled. When a plurality of self-blast circuit breakers
are combined in a battery of self-blast circuit breakers, a
common filling port 9 can be provided. The filling port 9
can be provided at a housing section extending transversely
with respect to a longitudinal axis of the self-blast
circuit breaker 1. The filling port 9 can be spaced from an
arcing chamber which surrounds the contact region of the
first contact 3 and of the second contact 4.
The use of self-blast circuit breakers as circuit breakers
has the advantage over conventional puffer circuit breakers
that a lower drive can be used. The additional
overpressure, produced by the evaporation of the burn-off
nozzle 11 and used for blowing the filling gas onto the
arc, saves drive energy for the compression of the filling
gas. However, it must be ensured that the burn-off nozzle
11 burns off only to such an extent that, in a renewed
switching operation, still sufficient material of the burn-
off nozzle 11 can evaporate. Moreover, for an efficient
pressure build-up in the heating volume, a clogging of the
nozzle should occur, which is no longer possible with a
nozzle diameter which is too large compared with the
flowing current. Thus, it must also be ensured that the
burn-off nozzle 11 burns off only to such an extent that an
efficient pressure build-up on heating is still possible.
In order to be able to determine the burn-off status of the
burn-off nozzle 11 non-invasively, in exemplary embodiments
of the invention a transient pressure profile is detected
and evaluated when the self-blast circuit breaker 1 without
electric load is switched into the open state. In so doing,
pressure waves develop in the interior of the self-blast
circuit breaker 1, and move through the filling gas at the
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speed of sound. These pressure waves are influenced by the
geometry of the burn-off nozzle 11. By recording the
transient pressure profile at a measuring position, for
example at the filling port 9, and by subsequent
evaluation, the state of the burn-off nozzle can be
inferred.
To detect the transient pressure profile which occurs in
response to a switching operation at the filling port 9, a
mobile diagnostic device 20 is used. As described in more
detail below, the mobile diagnostic device 20 is used to
detect a transient pressure profile which occurs at a
measuring position when the self-blast circuit breaker 1
without electric load is switched into the open state. The
transient pressure profile is evaluated in order to
determine a state of the burn-off nozzle 11. To determine
the state, it is possible to determine, in dependence on
the pressure profile, whether the burn-off nozzle 11 is
already burnt off to such an extent that an opening of the
housing 2 of the self-blast circuit breaker is required to
gain access to the interrupting chamber.
The mobile diagnostic device 20 can comprise a pressure
sensor 22. The pressure sensor 22 can be attached to the
filling port 9, which can be configured as a gas
connection. The pressure sensor 22 has mechanical coupling
elements 24 which allow a mechanical mounting to the
filling port 9. The mechanical coupling elements can be
adapted to the geometry of the filling port such that a
mechanical mounting to the filling port 9 is possible. The
pressure sensor 22 is configured such that, in the state
mounted to the filling port 9, it detects a pressure
prevailing in the interior of the housing 2 at the filling
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port 9. The pressure sensor 22 can be configured such that
it has a response time which ensures a temporally resolved
pressure detection with a high temporal resolution, for
example with a temporal resolution of several milliseconds.
If the filling port 9 is provided with a nonreturn valve,
the pressure sensor 22 has elements which, by opening the
nonreturn valve, ensure that the pressure sensor 22 can
detect the pressure prevailing in the interior of the
housing 2 at the filling port 9. The pressure sensor 22 is
coupled to an interface 26 of a mobile measuring device 21.
The pressure sensor 22 can be detachably coupled to the
interface 26 of the mobile measuring device 21.
The mobile diagnostic device 20 comprises the mobile
measuring device 21. The mobile measuring device 21 can be
configured as a portable computer which is configured in
terms of programming to evaluate the pressure as a function
of time prevailing in the interior of the housing 2, in
order to determine the state of the burn-off nozzle 11. The
mobile measuring device 21 has a control 25 which can
comprise one or more processors. The control 25 is coupled
to the interface 26 in order to receive from the pressure
sensor 22 a signal or data which indicate the pressure
profile at the filling port 9. The control 25 processes the
data in order to evaluate a pressure profile in a time
interval after the switching operation. The time interval
can, for example, have a duration of several milliseconds,
several tens of milliseconds or several hundreds of
milliseconds. The control 25 can perform various processing
steps in order to automatically infer the state of the
burn-off nozzle 11 from the detected pressure profile. For
this purpose, the control 25 can, for example, integrate a
pressure variation in a time interval or determine spectral
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components of the pressure profile by calculation.
Alternatively or additionally, the control 25 can compare
the pressure profile as function of time with one or more
reference curves. Depending on the evaluation of the
pressure profile, the control 25 can automatically
determine whether the burn-off of the burn-off nozzle has
progressed to such an extent that the interrupting chamber
of the self-blast circuit breaker 1 has to be opened in
order to subject the burn-off nozzle 11 to a visual
inspection.
The mobile measuring device 21 can have a user interface
29. A result of the evaluation of the pressure profile can
be output by the control 25 via the user interface 29
and/or stored in a memory 27 of the mobile measuring device
21.
In order to take account of the fact that self-blast
circuit breakers exist with different geometry and
configuration, the user can input information via the user
interface 29 which relates to the self-blast circuit
breaker 1 and which is used by the control 25 in the
automatic evaluation of the detected pressure profile. For
example, the mobile measuring device 21 can be configured
such that the user can specify a model designation of the
self-blast circuit breaker via the user interface 29, for
example by selecting from a predetermined group of models.
The memory 27 contains for the different models or
construction types respective reference data with which the
control 25 can evaluate the detected pressure profile to
determine the state of the burn-off nozzle 11. The
reference data stored in the memory 27 can have different
formats depending on the processing of the detected
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pressure profile which is performed by the control 25. If,
for example, the control 25 determines a single
characteristic quantity from the detected pressure profile
by temporal integration or spectral analysis of the
pressure profile, there can be stored in the memory 27 for
each of a plurality of construction types a respective
threshold value. Based on a comparison of the
characteristic quantity determined from the pressure
profile with the threshold value, the control 25 can
automatically determine whether the burn-off of the burn-
off nozzle 11 has progressed to such an extent that the
housing 2 of the self-blast circuit breaker has to be
opened. If the control 25 determines from the detected
pressure profile, for example by spectral analysis of the
pressure profile, a plurality of characteristic quantities
which can correspond to the spectral components, there can
be stored in the memory 27 for each of a plurality of
construction types a respective plurality of threshold
values with which the control 25 can evaluate the detected
pressure profile. In a further configuration, there can be
stored in the memory 27 for each of a plurality of
construction types of self-blast circuit breakers a
respective plurality of characteristic transient pressure
profiles. The control 25 can compare the detected pressure
profile in the time domain with the characteristic
transient pressure profiles stored in the memory 27, in
order to automatically determine whether the burn-off of
the burn-off nozzle 11 has progressed to such an extent
that the housing 2 of the self-blast circuit breaker has to
be opened.
Alternatively or additionally, the mobile measuring device
21 can also archive transient pressure profiles which are
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detected after a switching operation without electric load
in a plurality of maintenance procedures on the self-blast
circuit breaker which has just been inspected. An
evaluation of the detected pressure profile for determining
the nozzle burn-off can take place based on a comparison
with pressure profiles which have been detected in earlier
maintenance procedures on the self-blast circuit breaker 1.
Based on the variation of the detected pressure profile,
the control 25 can infer an increasing burn-off of the
burn-off nozzle 11 and automatically determine whether the
interrupting chamber of the self-blast circuit breaker 1
has to be opened. In such a diagnosis which is based on the
historical data of the respective self-blast circuit
breaker 1, the user can input via the user interface 29
information which uniquely identifies the self-blast
circuit breaker 1.
If a plurality of self-blast circuit breakers are combined
in a battery having a common filling port, the control 25
can perform the evaluation separately for each of the
plurality of self-blast circuit breakers. The pressure
variation prevailing at the filling port in the interior of
the housing depends generally on which of the plurality of
self-blast circuit breakers is switched into the open
state, since the pressure waves in the filling gas have to
travel over different paths from the nozzle region of the
corresponding self-blast circuit breaker to the filling
port. Accordingly, there can be stored in the memory 27 for
each of the plurality of self-blast circuit breakers of a
battery of self-blast circuit breakers data which allows an
evaluation of the pressure profile detected in response to
a switching operation of the corresponding self-blast
circuit breaker at the filling port, in order to determine
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the state of the burn-off nozzle of the corresponding self-
blast circuit breaker.
The mobile diagnostic device 20 can have further
components. The beginning and end of a time interval, in
which the geometry of the burn-off nozzle 11 can be
inferred from the transient pressure profile in the
interior of the housing 2, depend on when the switching
operation is triggered. To determine this time, a further
sensor 23 or a plurality of further sensors can be
provided. The further sensor 23 can monitor a drive of the
self-blast circuit breaker and/or measure an electrical
resistance, voltage drop or current between the contacts 3
and 4. The further sensor 23 can, for example, be
configured as a rotation angle sensor which monitors a
rotation angle of the drive shaft 6. The further sensor 23
can be detachably coupled to a further interface 28 of the
mobile measuring device 21. The control 25 can use the data
detected by the further sensor 23 to determine the time of
a contact separation of the contacts 3 and 4 of the self-
blast circuit breaker. The control 25 can use this time to
begin a recording of a pressure profile and/or to select,
from a pressure profile detected by the pressure sensor 22
over a longer period of time, a part which represents the
transient pressure profile after the switching operation
and provides information about the burn-off of the burn-off
nozzle 11.
FIG. 2-4 illustrate the construction of an arcing chamber
of a self-blast circuit breaker, in which the method and
the mobile diagnostic device according to exemplary
embodiments can be used. FIG. 2-4 show cross-sectional
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views along the longitudinal axis of the self-blast circuit
breaker.
In the interior of the housing 2 of the self-blast circuit
breaker 1, a compression volume 15 and a heating volume 16
are provided. The compression volume 15 and the heating
volume 16 can be connected by a nonreturn valve 17. The
compression volume 15 and the heating volume 16 are gas
compartments formed in the interior of the housing 2. The
contacts of the switch comprise a finger contact 4 and a
contact pin 3. Other configurations of the contacts can be
used. The burn-off nozzle 11, which is composed of an
insulant, is connected to the finger contact 4. The heating
volume 16 is in a fluid connection, via a passage 12, with
an opening 10, at which, for example in the case of a
short-circuit breaking, the arc can be subjected to a flow
of the filling gas. Depending on the design of the switch,
a plurality of such passages 12 may also be provided.
When the self-blast circuit breaker 1 is switched into the
open state, the switching action causes a volume reduction
of the compression volume 15. The pressure in the
compression volume 15 and heating volume 16 rises. When the
nozzle region of the burn-off nozzle 11 is freed by the
relative movement between the finger contact 4 and the
contact pin 3, a flow begins in which the gas flows into
the nozzle region via the passage 12. By the end of the
switching operation, a stagnation point forms at the place
where the gas flow flows out of the heating volume 16 via
the passage 12 into the nozzle region. Also in spaced
regions of gas volume in the interior 8 of the self-blast
circuit breaker 1, the resulting pressure waves in the
filling gas lead to a transient pressure variation. This
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can be monitored at a measuring position, for example at
the filling port 9.
FIG. 3 and FIG. 4 show an enlarged cross-sectional view of
the nozzle region which is formed by the burn-off nozzle
11. When the self-blast circuit breaker 1 under electric
load is switched into the open state, an arc burning
between the contacts 3 and 4 causes the burn-off nozzle 11
to evaporate at its radially inner region in order to
support the pressure build-up for blowing the filling gas
onto the arc. Owing to the burning-off of the burn-off
nozzle 11, the nozzle geometry widens radially, as
illustrated schematically in FIG. 3 by arrows. FIG. 4 shows
the nozzle region after a plurality of switching operations
under load. The changing nozzle geometry influences the
propagation of sound waves or other pressure waves in the
filling gas during a switching operation. The different
pressure profiles, depending on the state of the burn-off
nozzle 11, which can be observed for example at the filling
port 9 in the gas volume, allow the determination of the
state of the burn-off nozzle from the detected pressure
profile.
FIG. 5 shows schematically pressure profiles which occur at
a measuring position of the self-blast circuit breaker 1
after a switching operation into the open state without
load. In this case, the pressure profile 41 illustrated by
a dashed line corresponds to a system without nozzle burn-
off. The pressure profile 42 illustrated by a continuous
line corresponds to a system in which the burn-off nozzle
11 is radially burnt off to such an extent as is the case
in typical self-blast circuit breakers after approximately
eight short-circuit breaking instances.
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FIG. 5 shows the transient pressure profile which results
at a measuring position spaced from the nozzle region of
the self-blast circuit breaker. The measuring position can,
for example, be arranged at the axial end of the self-blast
circuit breaker. The transient behaviour over a period of
time totalling 50 ms is illustrated. The illustrated
pressure profiles were determined for a typical filling
pressure and a typical contact speed in the switching
operation.
The detected pressure profile at the measuring position,
for example at the filling port 9, exhibits substantial
differences depending on the extent to which the nozzle is
burnt off. At the beginning of the switching action, the
transient pressure profile 41 in a self-blast circuit
breaker without nozzle burn-off and the transient pressure
profile 42 in a self-blast circuit breaker with nozzle
burn-off exhibit the same profile as a function of time.
The pressure profile 41 in the self-blast circuit breaker
without nozzle burn-off rises subsequently and settles
around an increased value. The pressure profile 42 in the
self-blast circuit breaker with nozzle burn-off exhibits a
completely different behaviour. After reaching a first
local maximum, the pressure falls below the initial
pressure, which corresponds to the filling pressure. The
pressure difference between the two pressure profiles 41
and 42 in the present example reaches a value, illustrated
at 46, which occurs after a time of several milliseconds or
several tens of milliseconds, for example after
approximately 40 ms. Only subsequently does the pressure
profile 42 rise in the self-blast circuit breaker with
CA 02889300 2015-04-23
nozzle burn-off and approach the pressure profile 41 in the
self-blast circuit breaker without nozzle burn-off.
The different pressure profiles can be automatically
detected in methods and mobile diagnostic devices according
to exemplary embodiments. For this purpose, for example,
the pressure profile, detected in a time interval 43 after
the beginning of the switching action, is analysed. Various
processing steps can be performed for this purpose, such as
temporal integration of the pressure variation with respect
to the filling pressure, spectral analysis in the interval
43 and/or direct comparison of the pressure profiles 41 and
42 which are detected in the time interval 43. A start time
44 and an end time 45 of the time interval can be set in
dependence on the time tT at which the contact separation
takes place. The electrode burn-off of the contacts 3 and 4
of the self-blast circuit breaker can be taken into account
here. Alternatively or additionally, the time interval 43
can also be set in dependence on the speed of sound in the
filling gas and in dependence on the geometry of the self-
blast circuit breaker 1. In this way, the propagation time
of the pressure waves from the nozzle region to the
measuring position, i.e. for example to the filling port 9,
can be taken into account.
Different transient pressure profiles in dependence on the
state of the burn-off nozzle can also be observed in
variations in the parameters of the self-blast circuit
breaker, for example for different filling pressures,
different contact speeds or different electrode burn-off.
The methods and devices according to exemplary embodiments
can thus also be used while taking into account boundary
conditions which change on use in the field, such as
CA 02889300 2015-04-23
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filling pressure fluctuations, electrode burn-off or
changing contact speeds. While these parameters only weakly
influence the pressure profile at the measuring position,
for example at the filling port, resulting in response to a
switching operation without electric load, the transient
pressure profile exhibits substantial differences in
dependence on the nozzle burn-off.
FIG. 6 and FIG. 7 shows pressure profiles which occur at a
measuring position of the self-blast circuit breaker 1
after a switching operation into the open state without
load. In this case, the pressure profile 51 and 56,
respectively, illustrated by a dashed line corresponds to a
system without nozzle burn-off. The pressure profile 52 and
57, respectively, illustrated by a continuous line
corresponds to a system in which the burn-off nozzle 11 is
radially burnt off to such an extent as is the case in
typical self-blast circuit breakers after approximately
eight short-circuit breaking instances. The transient
behaviour over a period of time totalling 50 ms is
illustrated. The curves were determined for a typical
contact speed in the switching operation.
In contrast to the pressure profiles illustrated in FIG. 5,
the pressure profiles for other filling pressures,
illustrated in FIG. 6 and FIG. 7, are determined. The
pressure profile 51 illustrated in FIG. 6 for a self-blast
circuit breaker without nozzle burn-off and the pressure
profile 52 for a self-blast circuit breaker with nozzle
widening were determined for a filling pressure 50 which is
greater than the filling pressure 40 in FIG. 5. The
pressure profile 56 illustrated in FIG. 7 for a self-blast
circuit breaker without nozzle burn-off and the pressure
CA 02889300 2015-04-23
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profile 57 for a self-blast circuit breaker with nozzle
widening were determined for a filling pressure 55 which is
greater than the filling pressure 40 in FIG. 5 and than the
filling pressure 50 in FIG. 6.
The substantial differences in the pressure profile in
dependence on the state of the burn-off nozzle, which are
explained with reference to FIG. 5, can be observed for
various filling pressures. The detected pressure profile
for a system without or with low nozzle burn-off can be
reliably differentiated from the detected pressure profile
for a system with more severe nozzle burn-off, for example
after a plurality of short-circuit breaking instances. A
non-invasive determination of the nozzle burn-off based on
the detected pressure profile is robust to variations of
the filling pressure.
A change of the contact speed, with which the contacts 3
and 4 of the self-blast circuit breaker in a switching
operation are moved relative to one another, can influence
the behaviour of the transient pressure profile at the
measuring position. The characteristic differences, which
exist in the transient pressure profile in response to a
switching operation between a self-blast circuit breaker
without nozzle burn-off and a self-blast circuit breaker
with nozzle burn-off, can be observed for different contact
speeds.
FIG. 8 and FIG. 9 illustrate the transient pressure profile
at the measuring position when the switching action takes
place with different contact speeds. The transient
behaviour over a period of time totalling 50 ms is
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illustrated. The pressure profiles were determined for a
typical filling pressure 60.
FIG. 8 shows the transient pressure profile at the
measuring position for a self-blast circuit breaker without
nozzle burn-off. The pressure profile 61, illustrated by a
dashed line, at the measuring position was determined for a
typical contact speed in the switching operation. The
pressure profile 63, illustrated by a dotted line, at the
measuring position was determined for a contact speed which
is approximately 40% greater than the contact speed in the
pressure profile 61.
FIG. 9 shows the transient pressure profile at the
measuring position for a self-blast circuit breaker with
nozzle burn-off which has resulted in a widening of the
nozzle diameter by 4 mm. The pressure profile 62,
illustrated by a continuous line, at the measuring position
was determined for a typical contact speed in the switching
operation. The pressure profile 64, illustrated by a dash-
dot line, at the measuring position was determined for a
contact speed which is approximately 40% greater than the
contact speed in the pressure profile 62.
The contact speed influences the pressure as a function of
time detected at the measuring position. In the case of a
self-blast circuit breaker without nozzle burn-off, the
pressure profile 61 for a lower contact speed initially
exhibits a less steep rise than the pressure profile 63 for
a higher contact speed. In both cases, the pressure profile
exhibits oscillations and finally levels out at an
increased value. In the case of a self-blast circuit
breaker with nozzle burn-off, the pressure profile 64
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exhibits for a higher contact speed initially a steeper
rise than the pressure profile 62 determined for the lower
contact speed. The subsequent pressure drop in the pressure
profile 64 for the higher contact speed is also more
pronounced and takes place more quickly than in the
pressure profile 62 for the lower contact speed.
Despite the influence which the contact speed of the self-
blast circuit breaker has on the transient pressure profile
at the measuring position, the characteristic differences
between the transient pressure profile in the case of a
self-blast circuit breaker without or with low nozzle burn-
off and a self-blast circuit breaker with more severe
nozzle burn-off remain. A non-invasive determination of the
nozzle burn-off based on the detected pressure profile can
be reliably performed also in the case of self-blast
circuit breakers with different contact speeds.
Further investigations on self-blast circuit breakers show
that an electrode burn-off of the first contact 3 and/or of
the second contact 4 of the self-blast circuit breaker 1
only weakly influences the pressure profiles detected at
the measuring position. The characteristic differences
which exist in the transient pressure profile in response
to a switching operation between a self-blast circuit
breaker without nozzle burn-off and a self-blast circuit
breaker with nozzle burn-off can even be observed when the
contacts 3 and 4 of the self-blast circuit breaker 1 are
altered by nozzle burn-off. A non-invasive determination of
the nozzle burn-off based on the detected pressure profile
can be reliably performed also in the case of self-blast
circuit breakers which exhibit different electrode burn-
off.
CA 02889300 2015-04-23
FIG. 10 is flow diagram of a method 70 according to an
exemplary embodiment. The method can be automatically
performed by the mobile diagnostic device 20 which was
explained with reference to FIG. 1. The method 70 can be
performed during maintenance of the assembled self-blast
circuit breaker. For this purpose, the mobile diagnostic
device 20 can be installed on the self-blast circuit
breaker after the self-blast circuit breaker has been
isolated.
At 71 a switching operation of the self-blast circuit
breaker without electric load is triggered. In the
switching operation, the self-blast circuit breaker can be
switched from the closed state into the open state.
At 72 a time-dependent pressure profile which results in
response to the switching operation is detected at a
measuring position. The measuring position can be a filling
port for filling the self-blast circuit breaker with
filling gas.
At 73 the detected pressure profile is evaluated. For this
purpose, the pressure profile detected in the time domain
can be compared with at least one reference curve which is
stored in the mobile diagnostic device 20, in order to
determine the state of the burn-off nozzle. Alternatively
or additionally, the pressure profile detected in a time
interval after triggering of the switching operation can be
subjected to various data processing procedures in order to
determine the state of the burn-off nozzle. For example, a
pressure variation with respect to a filling pressure in
the time interval can be integrated over time to reliably
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determine whether the pressure at the measuring position
increases or decreases during the time interval.
Alternatively or additionally, a frequency spectrum of the
pressure profile, which exhibits the pressure profile
during the time interval, can be determined. The start time
and end time of the time interval for which the transient
pressure profile is evaluated can be set in dependence on
the time of the contact separation of the self-blast
circuit breaker in the switching operation, which is
triggered at 71. The circuit breaker geometry and speed of
sound in the filling gas can be taken into account in the
setting of the time interval. The start time of the
relevant time interval in which the detected pressure can
reliably provide information about the nozzle burn-off can
be determined from the time of the contact separation and
the propagation time of the pressure wave, which is in
dependence on the speed of sound and the length of path
between nozzle region and measuring position. The transient
pressure profile at the measuring position, which can
provide information about the nozzle burn-off, can die out
in a time of several tens of milliseconds to several
seconds. Accordingly, the time interval for which the
transient pressure profile is evaluated can have a duration
of less than one second, in particular of less than 500 ms,
in particular of less than 100 ms. An observation and
evaluation of the pressure profile can also take place over
longer time intervals. As was described with reference to
FIG. 5-9, however, the state of the burn-off nozzle can be
inferred already from the transient behaviour which can be
observed, for example, in a period of time of 50 ms.
At 74-76 it can be determined, in dependence on the
evaluation of the pressure profile at 73, what state the
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burn-off nozzle is in. In this case, as illustrated for the
method 70, it can be determined whether a disassembly of
the self-blast circuit breaker is required. At 74 it can be
determined whether the nozzle burn-off is greater than a
threshold value. For this purpose, a characteristic
quantity determined at 73 from the transient pressure
profile can be compared with a threshold value.
If at 74 it is determined that the nozzle burn-off has not
yet progressed to such an extent that an interrupting
chamber of the self-blast circuit breaker has to be opened
for a visual inspection of the burn-off nozzle, a
corresponding diagnosis result can be output at 75. For
example, information that no disassembly of the self-blast
circuit breaker is required can be output via a user
interface.
If at 74 it is determined that the nozzle burn-off has
progressed to such an extent that an interrupting chamber
of the self-blast circuit breaker has to be opened for a
visual inspection of the burn-off nozzle, a corresponding
diagnosis result can be output at 76. For example,
information that the self-blast circuit breaker has to be
disassembled can be output via a user interface.
At 77 a logging of the pressure profile measurement by the
mobile diagnostic device can take place. For this purpose,
the detected transient pressure profile at the measuring
position after triggering the switching operation and/or a
characteristic quantity determined from the transient
pressure profile can be stored in a memory of the mobile
diagnostic device. The pressure profile measurement and/or
the associated log can be archived.
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The mobile diagnostic device can be removed from the self-
blast circuit breaker after performing the method and
mounted on a further self-blast circuit breaker for renewed
performance of the method. Thus, for a plurality of self-
blast circuit breakers, during the maintenance of the
corresponding self-blast circuit breakers, in each case the
state of the burn-off nozzle can be determined.
While exemplary embodiments have been described with
reference to the figures, modifications can be carried out
in further exemplary embodiments.
For example, the methods and mobile diagnostic devices can
also be used when a plurality of self-blast circuit
breakers are combined in an arrangement or "battery" of
self-blast circuit breakers which has a common filling port
and/or a common drive shaft. In this case, the different
circuit breakers are switched into the open state in
parallel by the drive shaft. The transient pressure profile
respectively measured at the filling port as measuring
position can be evaluated in order to determine the state
of the burn-off nozzle for each of the plurality of self-
blast circuit breakers.
Further sensors can be used to perform the diagnosis of the
self-blast circuit breaker. For example, a resistance,
voltage drop or current between the contacts of the self-
blast circuit breaker can be measured to determine the time
at which the contact separation takes place. In dependence
on the time thus determined, a recording of the pressure
profile which is detected at the measuring position can be
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triggered and/or a time interval, for which the detected
pressure profile is further evaluated, can be set.
While the diagnosis can be performed such that it is only
determined whether the self-blast circuit breaker is to be
disassembled and the housing opened for an inspection of
the burn-off nozzle, the diagnosis can also quantitatively
determine the state of the burn-off nozzle. For example,
the transient pressure profile which is detected in the
diagnosis at the measuring position can also be evaluated
in order to quantitatively determine the nozzle burn-off
therefrom. For this purpose, a comparison can be made with
characteristic diagrams or other tables, in which for the
respective construction type of the self-blast circuit
breaker the resulting pressure profiles in dependence on
the nozzle burn-off are stored.
With the aid of methods and diagnostic devices according to
exemplary embodiments, the state of the burn-off nozzle of
a self-blast circuit breaker can be determined non-
invasively in the course of a maintenance on the self-blast
circuit breaker. A time- and cost-intensive opening of the
housing of the self-blast circuit breaker in a workshop can
thus be avoided. The methods and diagnostic devices provide
a means with which the life expectancy or time until the
next inspection of a self-blast circuit breaker can be
reliably determined and thereby an efficient use of the
self-blast circuit breaker in the electrical energy supply
network ensured.
Self-blast circuit breakers are widely used today in the
electrical energy supply networks of the high- and extra-
high-voltage level. Exemplary embodiments of the invention
CA 02889300 2015-04-23
can thus support the maintenance and servicing strategy of
energy suppliers or network operators.
